Long range atmospheric transport is an important pathway for the spread of plant pathogens, such as rust fungi which can devastate cereal crop health and food security worldwide. In recent years, serious concern has been caused by the evolution of new virulent races of Puccinia graminis f. sp. tritici, a pathogen causing wheat stem rust that can result in close to 100% yield losses on susceptible wheat cultivars in favourable weather conditions. We applied an Earth system model to compare the suitability of the current climate and a business-as-usual climate scenario (RCP 8.5) for 2100 for wheat stem rust. Although there are large uncertainties in modelling changes in disease spread, we focus in this paper on the changes which are likely to be robust to model assumptions. We show that the warmer climate with lower relative humidity and enhanced turbulence will lead to ∼40% increase in the urediniospore emitting potential of an infected field as global average. The main predicted changes in the atmospheric long-range transport include reduced connections between Europe, Africa and South Asia, and increased frequency of spores crossing the mid-latitude oceans. Due to reduction in subfreezing conditions, the overwintering areas of the fungus will expand. On the other hand, projected drier conditions will reduce substantially the probability of an infection starting from deposited spores, except in irrigated fields.

SummarySwitchgrass (Panicum virgatum) is a promising biofuel crop native to the United States with genotypes that are adapted to a wide range of distinct ecosystems. Various plants have been shown to undergo symbioses with plant growth‐promoting bacteria and fungi, however, plant‐associated microbial communities of switchgrass have not been extensively studied to date. We present 16S ribosomal RNA gene and internal transcribed spacer (ITS) data of rhizosphere and root endosphere compartments of four switchgrass genotypes to test the hypothesis that host selection of its root microbiota prevails after transfer to non‐native soil. We show that differences in bacterial, archaeal and fungal community composition and diversity are strongly driven by plant compartment and switchgrass genotypes and ecotypes. Plant‐associated microbiota show an enrichment in Alphaproteobacteria and Actinobacteria as well as Sordariales and Pleosporales compared with the surrounding soil. Root associated compartments display low‐complexity communities dominated and enriched in Actinobacteria, in particular Streptomyces, in the lowland genotypes, and in Alphaproteobacteria, specifically Sphingobium, in the upland genotypes. Our comprehensive root analysis serves as a snapshot of host‐specific bacterial and fungal associations of switchgrass in the field and confirms that host‐selected microbiomes persist after transfer to non‐native soil.

Ergot alkaloids are mycotoxins that affect the nervous and reproductive systems of exposed individuals through interactions with monoamine receptors. They have been studied more widely in ergot fungi and grass endophytes but also are found in Aspergillus fumigatus, an opportunistic human pathogen that reproduces and disseminates exclusively through conidia. The ergot alkaloids festuclavine and fumigaclavines A, B and C are present in or on conidia of A. fumigatus. Cultures of the fungus that are free of conidia are difficult to obtain, obscuring comparisons of conidia versus vegetative hyphae as sources of the ergot alkaloids. To create conidiation-deficient strains of A. fumigatus we manipulated the bristle A gene (brlA), which controls vesicle formation or budding growth necessary for conidiation in Aspergillus spp. Disruption of brlA in A. fumigatus, via homologous recombination, resulted in a nonconidiating mutant that produced bristle-like structures instead of conidiophores and conidia. Moreover the disrupted strain failed to produce ergot alkaloids as verified by HPLC analyses. Complementation with a wild-type allele restored conidiation and ergot alkaloid production. These results suggest that ergot alkaloids are not produced within the vegetative mycelium of the fungus and are associated directly with conidiation.

Ergot alkaloids are mycotoxins that affect the nervous and reproductive systems of exposed individuals through interactions with monoamine receptors. They have been studied more widely in ergot fungi and grass endophytes but also are found in Aspergillus fumigatus, an opportunistic human pathogen that reproduces and disseminates exclusively through conidia. The ergot alkaloids festuclavine and fumigaclavines A, B and C are present in or on conidia of A. fumigatus. Cultures of the fungus that are free of conidia are difficult to obtain, obscuring comparisons of conidia versus vegetative hyphae as sources of the ergot alkaloids. To create conidiation-deficient strains of A. fumigatus we manipulated the bristle A gene (brlA), which controls vesicle formation or budding growth necessary for conidiation in Aspergillus spp. Disruption of brlA in A. fumigatus, via homologous recombination, resulted in a nonconidiating mutant that produced bristle-like structures instead of conidiophores and conidia. Moreover the disrupted strain failed to produce ergot alkaloids as verified by HPLC analyses. Complementation with a wild-type allele restored conidiation and ergot alkaloid production. These results suggest that ergot alkaloids are not produced within the vegetative mycelium of the fungus and are associated directly with conidiation.

Freezing tolerance, reproductive development, and seed germination of jack pine (Pinus banksiana Lamb.) and pitch pine (Pinus rigida Mill.) were compared in a small sympatric population in Acadia National Park in Maine, at the southern range limit of the former and the northern limit of the latter. Freezing tolerances of vegetative shoots and roots were similar for both species. Both species flower prolifically, and there was no evidence of differences in either pollen viability, cone survival, or proportion of viable seed (65–70% of the total). Regeneration success (established seedlings ranging from 1 to 13 years old) was similar overall for both species, but success by species varied greatly in some years. Jack pine regeneration was significantly associated with thinner soils, while pitch pine regeneration was associated with thicker soils in hollows. Jack pine seed germinated significantly faster than pitch pine seed, especially when day–night temperature was reduced. Pitch pine seedlings always exhibited a significantly higher shoot/root ratio than those of jack pine. The most northerly provenances of jack pine germinated significantly faster than those from the most southerly provenances. Jack pine also germinated at a significantly higher percentage than pitch pine in exposed granite sand. Thus relatively cool, dry conditions may favor establishment of jack pine seedlings, while pitch pine establishment may be favored in warmer, wetter conditions.